Genes and Genetic Disorders PSY 104 October 29, 2011 Genes and Genetic Disorders When answering the question, “How does a child develop? ” it is impossible to determine each individual influence that decides who a child becomes (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). What can be determined are the most obvious influences, which are genetics, parenting, experiences, friends, and family relationships. These factors play the biggest roles in a child’s development, and can be combined in an infinite number of ways (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005).
As a child develops, a mixture of genetic inheritance and life experience shapes the person that he grows up to be. The exact recipe of that mixture, though, is unknown and has puzzled philosophers, psychologists, and educators for hundreds of years (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). This is the nature versus nurture debate, and it asks the question, “Are we the result of nature (our genetic background) or nurture (our environment)? ” (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005).
From the moment a child is born, nurturing joins nature in the role of shaping who the child is and who he will become (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). Nature, though, begins doing its job at the moment of conception. Genetics is the science of inheritance and its goal is to understand the method by which two parents influence the traits of an offspring, and to understand how abnormalities can contribute to genetic disorders, such as Huntington’s Disease.
Genes play a vital role in determining a person’s physical traits and health. A person’s genetic code is established when the mother’s egg, or ovum, combines with the father’s sperm (Mossler, 2011). The ovum and the sperm are called the sex or reproductive cells, and the cell that is formed after their union is comprised of duplication instructions that will ultimately turn one cell into trillions of cells that contain the identical genetic code of the first (Mossler, 2011).
Within each cell are chromosomes which contain molecules that are called deoxyribonucleic acid (DNA). The DNA is wrapped together, and this forms the chromosomes, which store the genetic instructions on how to build the trillions of cells (Mossler, 2011). Most cells in the human body contain 23 pairs of chromosomes, thus forming a total of 46. The reproductive cells have just 23 unpaired chromosomes; therefore humans receive half of their chromosomes from ovum and the other half from the sperm cell (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005).
Boys inherit an X chromosome from their mothers and a Y chromosome from their fathers, while girls inherit an X chromosome from each parent (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). Chromosomes are held in the nucleus, which is located in the middle of a cell (Mossler, 2011). The DNA’s shape is a twisted, double helix shape, and the genes are little segments of DNA that carry hereditary information (Mossler, 2011). That information is what determines certain human traits like height or hair color (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005).
Adenine (A), thymine (T), cytosine (C), and guanine (G) are chemicals of DNA and they are threaded in patterns on fine, spiraled strands in the cell (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). These patterns are the codes for manufacturing proteins, which are chemicals that allow the body to function and regulate (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). Genes contain the directions for making protein products, such as pigments that give eyes their color (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005).
When cells copy themselves, they pass these directions to the new cells (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). Genes are either dominant or recessive, and dominant genes will always be present in a person even if there is only one copy of the gene in that pair (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). For a person to have a recessive disease or characteristic, the person must have the gene on both chromosomes of the pair (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005).
Sometimes changes or variants will occur in cells, and this can lead to gene mutation (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). Often, this is caused by aging cells or by exposure to certain chemicals or radiation, and cells usually recognize these mutations and repair themselves (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). But if the gene mutation occurs in egg or sperm cells, children can inherit the mutated gene from their parents (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005).
Although researchers have discovered thousands of diseases that are produced by genetic deviations, having a genetic mutation that causes a disease does not necessarily mean that a person will get that disease. (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). Most people carry anywhere from five to ten variant or disease genes in their cells, but these genes will only become an issue when the disease gene is dominant or when the same recessive disease gene exists on both chromosomes in a pair (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005).
Complications will also arise when several variant genes combine or are affected by environment (Hamosh, Scott, Amberger, Bocchini, & McKusick, 2005). When someone has a dominant gene for a disease, that person will usually get that disease and each of that person’s children will have a one in two (50%) chance of inheriting the gene and contracting the disease (Vonsattel & DiFiglia, 1998). This is called an autosomal dominant disorder, and an example of this disorder is Huntington’s Disease (Meiser & Dunn, 2000).
Huntington’s Disease is a brain disorder that destroys cells in the part of the brain that controls movement, emotion, and cognitive ability, thus affecting a person’s ability to think, talk, and move (Etchegary, 2009). Some symptoms of this disease are memory loss, depression, lack of impulse control, lack of coordination, twitching or other uncontrolled movements, and speech difficulty, and problems swallowing (Meiser & Dunn, 2000). These symptoms will occur between the ages of 30 and 50 (Vonsattel & DiFiglia, 1998). Huntington’s Disease is caused by a mutation in a gene on chromosome four (Vonsattel & DiFiglia, 1998).
The job of its protein product, huntingtin, is to direct the delivery of important molecules to the outside of the cell (Vonsattel & DiFiglia, 1998). The brain cells of patients affected by Huntington’s Disease accumulate clumps of protein that become toxic, resulting in cell death, and the patients can lose more than 25% of their brain cells before they die (Meiser & Dunn, 2000). There is no cure for Huntington’s Disease, but there are treatments that can help the patient more comfortable (Meiser & Dunn, 2000). In conclusion, genetics is the study of the plan of human life that is passed from generation to generation.
Deviations of these plans are necessary for evolution, but can cause disease. When there are alterations in one gene, or when several genes combine with environmental factors, genetic disorders like Huntington’s Disease can occur. And although nature and nurture work together to influence how a child develops, nature begins to do its job before nurture comes in. References Etchegary, H. (2009). Coping with Genetic Risk: Living with Huntington Disease (HD). Current Psychology, 28(4), 284-301. doi:10. 1007/s12144-009-9061-2. Hamosh, A. , Scott, A. F. , Amberger, J. S. , Bocchini, C. A. & McKusick, V. A. (2005). Online Mendelian Inheritance in Man (OMIM), a knowledgebase of human genes and genetic disorders. Nucleic Acids Research, 33(1), 112-121. doi:10. 1093/nar/gki033. Meiser, B. & Dunn, S. (2000). Psychological impact of genetic testing for Huntington’s disease: an update of the literature. Neurological Neurosurgery Psychiatry, 69(3), 574-578. Mossler, R. A. (2011). Child and adolescent development. Bridgepoint Education, Inc. Vonsattel, J. P. G. , & DiFiglia, M. (1998). Huntington disease. Journal of Neuroplathy and Experimental Neurology, 57(5). 369-384.